1. Field of the Invention
The present invention relates to a backlight module, and more particularly, to a backlight module for an image display device.
2. Description of Prior Art
Human beings see real-world images using both eyes. Further, the human brain forms so-called 3D images (three-dimensional images) according to differences in spatial distance between two views seen by both eyes from two different angles. A so-called 3D display is designed to create simulations of human visual fields from different angles to help users perceive 3D images when viewing 2D images.
Nowadays, 3D displays are divided into two kinds. One is auto-stereoscopic displays; the other is stereoscopic displays. Users of auto-stereoscopic displays are able to view 3D images without wearing glasses with a unique structure while ones of stereoscopic displays have to wear specially designed glasses to view 3D images.
The principle of a parallax barrier type auto-stereoscopic 3D display is to cast parallax images towards each eye of the observer to create a stereoscopic effect in the brain via an opaque parallax barrier. The principle of a spatial sequential type auto-stereoscopic 3D display is to cast a group of pixels towards the right eye and another different group of pixels towards the left eye via a time-irrelevant parallax barrier. Further, signals provided by the two groups of pixels are given to the right and left eyes, respectively, to provide the eyes different images. But, the spatial sequential type has a disadvantage that it only has half the original resolution. The principle of a time sequential type auto-stereoscopic 3D display is to cast the same group of the pixels towards both eyes at different time points by using a parallax barrier which is time-relevant and drives synchronously with a display panel. Further, a signal provided by the group of pixels is given to the right eye and the left eye at different time points to provide both eyes different images.
The persistence of vision of the human eye occurs for a moment of time once a frame rate is at higher than 40 Hz. Therefore, both the persistence of vision and a view of 3D image are realized by controlling the light produced by different backlight sources to enter the right and left eyes, respectively, and by switching backlight sources to match a frame rate of the display panel which achieves higher than 60 Hz through circuits and image processing.
However, to well control light-emitting angles of backlight sources is required in this technology, so the progress of backlight has to be precise. Refer to FIG. 1 and FIG. 2. FIG. 1 illustrates the light produced by a light emitting diode (LED) 12 of a conventional backlight module 10, and FIG. 2 illustrates a light guide plate 14 of the conventional backlight module 10. As shown in FIG. 1, the light guide plate 14 reflects the light emitted from the LED 12, which causes a crosstalk effect from various progresses of backlight and lowers the quality of three-dimensional images. To solve this problem, black coating 16 is applied to gapes of a side opposite to a side where the LED 12 is placed to absorb the light from the LED 12. But this invention has several disadvantages, such as a limited light emission angle from the LED 12, influenced brightness of the LED 12, and an enhanced hot spot effect. Besides, the light radiates from the center of the LED 12 so the light intensity around the intermediate axis (optical axis) is strongest. Symmetrically arranged black coating 16 cannot absorb the main reflective light produced by the LED 12, so that the light around the intermediate axis reflects, which enhances the hot spot effect, instead.